Connection error messages are unsafe: wrap them (#37329)

* Check that connection error msg are not unsafe

* Connection error messages are unsafe: wrap them

For example, in case of error, docker connection plugin returns exception
message containing Go template. These messages weren't tagged as unsafe
and were consequently rendered:

The conditional check 'result is failed' failed. The error was:
{
  'msg': u'Docker version check ([\'/usr/bin/docker\', \'version\', \'--format\', "\'{{.Server.Version}}\'"]) failed: Got permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock: Get http://%2Fvar%2Frun%2Fdocker.sock/v1.35/version: dial unix /var/run/docker.sock: connect: permission denied\n',
  'failed': True
}:
template error while templating string: unexpected '.'.
String: Docker version check (['/usr/bin/docker', 'version', '--format', "'{{.Server.Version}}'"]) failed: Got permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock: Get http://%2Fvar%2Frun%2Fdocker.sock/v1.35/version: dial unix /var/run/docker.sock: connect: permission denied

test/integration/targets/connection/plugin/dummy.py

@@ -0,0 +1,46 @@
+from __future__ import (absolute_import, division, print_function)
+__metaclass__ = type
+
+DOCUMENTATION = """
+    author:
+        - John Doe
+    connection: dummy
+    short_description: defective connection plugin
+    description:
+        - defective connection plugin
+    version_added: "2.0"
+    options: {}
+"""
+import ansible.constants as C
+from ansible.errors import AnsibleError
+from ansible.plugins.connection import ConnectionBase
+
+
+class Connection(ConnectionBase):
+
+    transport = 'dummy'
+    has_pipelining = True
+    become_methods = frozenset(C.BECOME_METHODS)
+
+    def __init__(self, play_context, new_stdin, *args, **kwargs):
+        super(Connection, self).__init__(play_context, new_stdin, *args, **kwargs)
+
+        raise AnsibleError('an error with {{ some Jinja }}')
+
+    def transport(self):
+        pass
+
+    def _connect(self):
+        pass
+
+    def exec_command(self, cmd, in_data=None, sudoable=True):
+        pass
+
+    def put_file(self, in_path, out_path):
+        pass
+
+    def fetch_file(self, in_path, out_path):
+        pass
+
+    def close(self):
+        pass